Search Publications
Determination of magnetic helicity content of solar active regions from SOHO/MDI magnetograms
Moon, Yong-Jae; Chae, Jongchul; Park, Young-Deuk
Chae (2001) first proposed a method of self-consistently determining the rate of change of magnetic helicity using a time series of longitudinal magnetograms only, such as taken by SOHO/MDI. Assuming that magnetic fields in the photosphere are predominantly vertical, he determined the horizontal component of velocity by tracking the displacements …
Helioseismology of Time-Varying Flows Through The Solar Cycle
Gizon, Laurent
Flows in the upper convection zone are measured by helioseismology on a wide variety of scales. These include differential rotation and meridional circulation, local flows around complexes of magnetic activity and sunspots, and convective flows. The temporal evolution of flows through cycle 23 reveals connections between mass motions in the solar …
Similarities and Differences between Coronal Holes and the Quiet Sun: Are Loop Statistics the Key?
Solanki, S. K.; Wiegelmann, T.
Coronal holes (CH) emit significantly less at coronal temperatures than quiet-Sun regions (QS), but can hardly be distinguished in most chromospheric and lower transition region lines. A key quantity for the understanding of this phenomenon is the magnetic field. We use data from SOHO/MDI to reconstruct the magnetic field in coronal holes and the …
About the rotation of the solar radiative interior
Henney, C. J.; Howe, R.; Eff-Darwich, A. +13 more
In the modern era of helioseismology we have a wealth of high-quality data available, e.g., more than 6 years of data collected by the various instruments on board the SOHO mission, and an even more extensive ground-based set of observations covering a full solar cycle. Thanks to this effort a detailed picture of the internal rotation of the Sun h…
Seismology of the solar atmosphere
Cacciani, Alessandro; Jefferies, Stuart M.; Finsterle, Wolfgang +4 more
We describe a new instrument for seismically probing the properties of the Sun's lower atmosphere, and present some first results from an observational campaign carried out at the geographic South Pole during the austral summer of 2002/2003. A preliminary analysis of the data (simultaneous, high-cadence observations of the velocity signals from th…
Motions of Flare Ribbons and Loops in Various Magnetic Configurations
Lin, Jun
Kopp-Pneuman-type magnetic configurations, which include a vertical current sheet, with various background fields are investigated. Dissipation of the current sheet as a result of magnetic reconnection produces bright flare ribbons on the solar disk and a growing flare loop system in the corona. In principle, the growth of flare loop system is gov…
New values of gravitational moments J2 and J4 deduced from helioseismology
Provost, J.; Berthomieu, G.; Irbah, A. +2 more
By applying the theory of slowly rotating stars to the Sun, the solar quadrupole and octopole moments J2 and J4 were computed using a solar model obtained from CESAM stellar evolution code (Morel, 1997) combined with a recent model of solar differential rotation deduced from helioseismology (Corbard et al., 2002). This model …
Dynamics and Structure of Supergranulation
Kosovichev, A. G.; Duvall, T. L., Jr.; Berrilli, F. +1 more
In this paper we investigate the temporal evolution and geometric properties of solar supergranular features. For this purpose we apply an automatic feature-tracking algorithm to a 6-day time series of 18 near-surface flowmaps containing 548 target objects. Lifetimes are calculated by measuring the time elapsing between the birth and death of each…
Multi-wavelength study of a high-latitude EUV filament
Heinzel, Petr; Schmieder, Brigitte; Schwartz, Pavol +1 more
A large filament was observed during a multi-wavelength coordinated campaign on June 19, 1998 in the Hα line with the Swedish Vacuum Solar Telescope (SVST) at La Palma, in the coronal lines Fe ix/x 171 Å and Fe xi 195 Å with the Transition Region and Coronal Explorer (TRACE) and in EUV lines with the SOHO/CDS spectrometer and the hydrogen Lyman se…
Measuring Stellar Differential rotation with asteroseismology
Solanki, Sami K.; Gizon, Laurent
The variation of rotation with latitude is poorly known on stars other than the Sun. Several indirect techniques, photometric and spectroscopic, have been used to search for departure from rigid rotation for sufficiently fast rotators. Here we investigate the possibility of measuring stellar differential rotation for solar-type stars through aster…